There are a few issues involved here.
The front wing must stall before the main wing,
which, in a lowdrag installation often is solved
by having wider chord on the rear wing (thus lower AR),
usually combined with higher loading on the front wing.
The same airfoil can be used, but low pitch airfoils are
most likely recommended.
According to Boeing research, refered to in one
of Darrol Stinton's books, the lowest drag
can be had for three-surface aircraft, where manouvering
is done with a conventional tail, but trimming is done
with the front wing.
As the front wing can only be used for pitch adjustments,
that is no ailerons or elevons, roll authority might be low.
Anhedral on the front wing might be wise, and dihedral
on the rear. Often you see sweep on the rear, combined
with wing-tip fins.
So sweet-stalling front wing, combined with low drag airfoils,
should result in a plane with low sink rate as the average
wing-loading is lower than a similar conventional plane.
Tord S Eriksson
www.tord.nu
Tord S Eriksson
www.tord.nu
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